Commonly used temperature sensors are Negative Temperature Coefficient (NTC) thermistors. These devices generate an output current that varies according to a nonlinear function with the sensed temperature of the environment in which they are installed.
There are numerous applications in which it is desirable to sense the temperature of an environment with a circuit capable of generating an electrical signal that varies linearly as a function of the temperature.
U.S. Pat. No. 5,068,595 discloses an adjustable temperature-dependent current generator having an adjustable linear relation to temperature. This prior current generator is based on a transconductance current multiplier, and comprises two temperature-dependent current generators.
U.S. Pat. No. 6,198,267 discloses a current generator that generates an output current substantially proportional to the absolute temperature of the base-emitter junctions of two bipolar transistors biased with respective constant currents. This current generator needs a switching network adapted to alternately connect one of the two bipolar transistors to the output node, through which the output current is delivered, and to disconnect the other transistor, and vice versa.
U.S. Pat. No. 4,947,057 discloses a mass fluid flow sensor with a circuit for compensating measurement fluctuations due to temperature variations of the fluid.
Prior temperature transducers are burdened by at least one of the following drawbacks: a temperature sensitive component is inserted in a feedback loop, therefore, temperature fluctuations alter the working point of the feedback loop and thus the loop gain, which may lead to instability of the loop; a plurality of relatively expensive components, such as thermistors, are required; and difficult to adjust over a broad range the gain of the temperature-current characteristic and the reference temperature at which the output current is null.